Digital Electronic Control of Automatic Ventilators

We have developed a digital system for use in ventilator control. The basic principle of this system is that every respiratory cycle is divided into a fixed number of counts. The control of the ratio of inspiration time to expiration time is accomplished by selecting a variable time out of the fixed time interval and designating it inspiration time. The remaining counts become expiration time. Respiratory rate is adjusted by varying the total time interval, and the ratio is adjusted by selecting a different inspiration time. The output of a digital-to-analog converter driven by the counters is adjustable and proportional to tidal volume. By inserting read only memories between the ratio scalars and the digital-to-analog converter input, a large number of different inspiration waveforms are generated.